What is the pH of a 0.50 M HF solution? a. 13.70 b. 10.53 c. 1.73 d. 0.30 Water

Question

What is the pH of a 0.50 M HF solution? a. 13.70 b. 10.53 c. 1.73 d. 0.30 Water and diethyl ether (CH_3CH_3OCH_2CH_3) are only slightly miscible because a. These liquids have very different densities. b. One compound is polar and the other is nonpolar. c. They both have polar bonds, but one is incapable of forming hydrogen bonds. d. Hydrogen bonding between the molecules increases solvent-solute interactions. The weaker the intermolecular forces in a substance a. the higher the boiling point. b. the lower the freezing point. c. the lower the vapor pressure. d. the larger the deviation from ideal gas behavior. Although BaSO_3 is not very soluble in water, it dissolves more readily in 0.10 M HCl because a. HCl is a weak acid. b. BaSO_3 is a weak base. c. BaSO_3 will form a complex ion. d. BaSO_3 will precipitate. Which conditions favor a low solubility of a gas in a liquid? a. high pressure, high temperature b. high pressure, low temperature c. low pressure, high temperature d. low pressure, low temperature

Explanation / Answer

Ans. 8. HF is a weak acid. Create an ICE table for calculating [H+] at equilibrium.

Now,

            Ka = [H+] [F-] / [HF]

            Or, 6.6 x 10-4 = (X) (X) / (0.5-X)

            Or, 6.6 x 10-4 x (0.5 -X) = X2

            Or. (3.3 x 10-4) – (6.6 x 10-4 X) = X2

            Or, X2 + 0.00066X – 0.00033 = 0

Solving the quadratic equation, we get two roost-

            X1 = - 0.0178            ; X2 = 0.01875

Since concentration can’t be negative, reject X1.

Therefore, X = 0.01875

Therefore, [H+] at equilibrium = 0.01875 M

Now,

pH = -log [H+] = -log 0.01875 = 1.73      

Therefore, correct answer is- C. 1.73

#9. Correct option D. Diethyl ether can’t form H-bonds with other molecules of same compound because it lacks a H-atom linked to a highly electronegative atom like O, N and F. Only H-atoms of water can form H-bond with O-atom of ether. This interaction is very unstable due to bulky hydrophobic regions on ether. So, the lower extent of H-bonding is responsible for little solubility of the two compounds.

One compound (water) is polar and the other (diethyl ether) is non-polar. Note that polar and non-polar solvents do not dissolve in each other- two compounds only dissolve when they have the same polarity.

Two compounds of same polarity mix well; those of different polarity do not mix well. In case both the compounds are polar, difference in density does not affect mixability. The same is true if both are non-polar, too.

Diethyl ether does not have a polar bond.

#10. Correct option B. Lower freezing point.

Weak intermolecular forces give lower boiling point (i.e. boils easily) and lower freezing point (i.e. freezes at much lower temperature). So, options A is incorrect while B is correct.

Vapor pressure. Lower intermolecular forces increase the relative number of free molecules escaping the solvent liquid phase to form the vapor phase. So, more free molecules are available in the vapor phase that yields higher vapor pressure.   

Ideal gas behavior assumed no interaction among molecules. So, weaker is the intermolecular attractions, least is the deviation from ideal behavior.

#11. 2 HCl + BaSO3(s) = BaCl2(s) + SO2(g) + H2O(aq)

HCl is a strong base.

Note the formation of H2O on product side. BaSO3 acts as a weak base in the reaction.

There is no formation of complex ion. See the reaction given above.

BaSO3 dissolves in HCl. The product BaCl2 is precipitated.

#12. Correct option- Low pressure and high temperature.

Lowe pressure and high temperature causes greater kinetic energy of gas molecules, so they easily escape from the solvent. It gives low solubility of gas.

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